Usually, the stress state of the crust can be caused by various geological processes, e.g., mantle convection, plate motions, volcanic eruptions and earthquakes. And it will induce temperature change in the earth's interior, especially in the crust. Based on thermos-elasticity theory, a convenient relationship between the temperature change (ΔT) and the sum of the change of the principle stresses (Δσ) can be described by the following equation:
                                          Δ            ⁢                                                  ⁢            T                    =                                                                      -                  α                                                  ρ                  ⁢                                                                          ⁢                                      c                    p                                                              ·                              T                0                            ·              Δ                        ⁢                                                  ⁢            σ                          ,                            (        1        )            where, T0 is the thermodynamic temperature; ρcp is the volumetric heat capacity at constant pressure; α is the coefficient of linear thermal expansion; Δσ denotes the change of the sum of the three principal stresses.
The magnitude of the temperature change in response to the stress change varies in different kinds of rock. Therefore, to determine the adiabatic stress derivative of the temperature (ΔT/Δσ) for different rocks, will help to understand the mechanism of temperature change of the earth's interior, and provide the theoretical basis for stress and temperature monitoring and earthquake prevention in active tectonic zones.
In the existing methods for determining the adiabatic stress derivative of the temperature, temperature sensors are usually attached to the surface of the rock samples and in contact with the air, such that the system is open to the external environment, and it is impossible to achieve instant loading and unloading due to the restriction of stress loading units. Thus, it is impossible to achieve stress loading and unloading under adiabatic condition and thereby the results of such determination will be affected significantly by the heat exchange between the rock sample and the air.
Deep sea, with a very high pressure, is a natural “high pressure pump”. On the other hand, within a time scale of 1-3 hours, deep sea water has very little fluctuation in temperature, which makes it an ideal thermostatic environment.